1. Field of the Invention
The invention relates to automotive vehicle powertrains, including a hybrid electric vehicle powertrain, with an engine connected driveably to torque input elements of multi-ratio transmission gearing without a hydrokinetic torque converter.
2. Background Art
In a conventional multiple-ratio power transmission mechanism for automotive vehicle powertrains, a hydrokinetic torque converter typically is disposed between an internal combustion engine and torque input elements of multiple-ratio gearing, which establishes multiple torque flow paths to vehicle traction wheels. The torque converter provides a torsional dampening effect that modifies dynamic disturbances during ratio shifting. It also effects smooth and improved launch performance of the vehicle from a standing start.
These advantages of a torque converter are partially offset by an inherent torque converter inefficiency, which results in a power loss manifested by a high operating temperature of the hydrokinetic torque converter fluid. This necessitates the use of an oil cooler. Further, the torque converter has a substantial rotary mass, including the mass of its hydraulic fluid, which adds to the gross weight of the transmission assembly. It also requires significant packaging space in the powertrain assembly.
Attempts have been made to eliminate the torque converter from the transmission to avoid inherent hydrokinetic power losses in the converter that reduce overall transmission efficiency. A control system for a converterless transmission of this type is disclosed in U.S. Pat. No. 6,299,565, which describes a strategy for obtaining maximum smoothness during a vehicle launch, as well as transient damping by a slipping wet clutch. The clutch is allowed to slip during engagement and disengagement of transmission ratio controlling friction elements.
A converterless transmission control system is disclosed also in U.S. Pat. No. 6,217,479, which discloses a strategy for slipping a friction element of a clutch and brake system for multiple-ratio gearing to achieve torsional isolation that normally would be provided by a hydrokinetic torque converter.
U.S. Pat. Nos. 6,176,808 and 6,585,066 disclose a converterless transmission in a hybrid electric vehicle powertrain wherein a high voltage induction motor is situated between an engine and multiple-ratio gearing. The motor is used to provide added vehicle launch performance and to reduce undesirable torsional vibrations during vehicle launch and during transmission ratio shifting. The rotor of the motor provides a rotary mass that achieves a flywheel effect analogous to the flywheel effect provided by a rotary torque converter in a conventional hydrokinetic torque converter transmission. U.S. Pat. No. 6,585,066 further discloses a slipping wet clutch in the power flow path between the engine and torque input elements of the gearing. The wet clutch complements the function of a damper assembly in transmission power flow paths, such as the power flow paths described in the '808 patent, by attenuating peak torque fluctuations during vehicle launch and during ratio shifts.
In a powertrain of the kind disclosed in the prior art references mentioned above, which are owned by the assignee of the present invention, a shift of the automatic transmission is characterized by two distinct shift phases, commonly referred to as a torque phase and an inertia phase. A power-on upshift, for example, experiences a torque phase when the capacity of the oncoming friction element is increased to control the shift. The output torque is changed to the upshifted torque while the speeds remain at the downshifted values. The torque phase is followed by an inertia phase in which the speeds of the engine and the transmission components are decreased to the upshifted values.
Normally, the torque phase is controlled using an open loop control system that is either event-based or time-based. Speed sensors within the transmission can detect the start of the inertia phase. When a speed ratio change is detected, the shift control system typically begins closed loop control of the oncoming friction element.
In a conventional transmission, only an input speed sensor and an output speed sensor are required since it is necessary only to obtain repetitive values of the speed ratio during the inertia phase to control shift events. The speed sensors determine the overall transmission ratio. Since the only event that is being controlled at any given instant is the shift event, the overall ratio is an indicator of the progress of the shift event. Thus, the speed ratio, or its derivative, is used as a control variable for closed loop control of the inertia phase and as a trigger for initiating other control events during the shift interval.
In a converterless multiple-ratio transmission of the kind previously discussed, such as the pre-transmission hybrid transmissions of the '066 patent and the '808 patent, it may be necessary, while a shift event is taking place, to control dynamic events other than the shift event. One example of a dynamic event that would be controlled during a shift event is disclosed in U.S. patent application Ser. No. 10/838,489 filed May 4, 2004, now U.S. Pat. No. 6,991,585, entitled “Torsional Isolation of a Converterless Automatic Transmission Through Slip Control of Friction Clutch.” That patent application is assigned to the assignee of this invention.
In a powertrain with a torsional isolation control strategy, for example, multiple clutches can be slipping so that the overall transmission ratio may not be indicative of the status of the shift event. Using transmission ratio percent shift complete as a control parameter, therefore, can cause errors by the shift controller, which can adversely affect shift quality. It is desirable, therefore, to use a strategy for controlling shift events that will accommodate accurate control of at least one additional simultaneous event.